An underlayment material is commonly used in a number of roofing applications as well as other underlayment situations. The typical product utilized in roofing underlayment is commonly referred to as “tar” of “felt” paper. The traditional “tar paper” is an asphalt impregnated paper product which is sold in a roll; unrolled on a roof; cut to length; and fastened to the roof utilizing staples or nails. Although tar paper is inexpensive, it does not seal nail holes through the paper and thus does not prevent water infiltration. In addition, once the felt is rolled out, it absorbs water and once wet, it wrinkles and expands, and must be allowed to dry out before covering with shingles. Other prior art shingle underlayment products also suffer from the same problems.
Accordingly, what is needed are generally low cost, heavyweight or lightweight, dimensionally stable underlayment products on which the installer can walk, without sticking or slipping, which will not slide underfoot and which will cold flow and/or elongate and recover to seal nail holes and other punctures. In addition, such products should be dimensionally stable, resist tearing, non-adhesive to other layers, and provide hot and cold flexibility.